Optical films and methods of making the same

ABSTRACT

Films for optical use, articles containing such films, methods for making such films, and systems that utilize such films, are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S.Provisional Patent Application Ser. No. ______, entitled “PRECISIONOPTICAL RETARDERS AND WAVEPLATES AND THE METHOD FOR MAKING THE SAME,”and filed on Apr. 15, 2004, the entire contents of which are herebyincorporated by reference.

TECHNICAL FIELD

This invention relates to optical films and related articles, systemsand methods.

BACKGROUND

Optical devices and optical systems are commonly used where manipulationof light is desired. Examples of optical devices include lenses,polarizers, optical filters, antireflection films, retarders (e.g.,quarter-waveplates), and beam splitters (e.g., polarizing andnon-polarizing beam splitters).

SUMMARY

This invention relates to films for optical use, articles containingsuch films, methods for making such films, and systems that utilize suchfilms.

In a first aspect, the invention features a method that includesproviding an article that includes a layer of a first material, whereinthe layer of the first material includes at least one trench and whereinthe layer is birefringent for light of wavelength λ propagating throughthe layer along an axis, wherein λ is between 150 nm and 2,000 nm, andfilling at least about 50% of a volume of the trench by sequentiallyforming a plurality of monolayers of a second material within thetrench.

In another aspect, the invention features a method that includes forminga layer of a material on a surface of a grating using atomic layerdeposition.

In another aspect, the invention features a method that includes formingan optical retardation film using atomic layer deposition.

In another aspect, the invention features an article, which includes acontinuous layer including rows of a first material alternating withrows of a nanolaminate material, wherein the continuous layer isbirefringent for light of wavelength λ propagating through thecontinuous layer along an axis, wherein λ is between 150 nm and 2,000nm.

In another aspect, the invention features an article including a formbirefringent optical retardation film that includes a nanolaminatematerial.

Embodiments of the invention can include one or more of the followingfeatures.

The filling can further include forming one or more monolayers of athird material within the trench, wherein the second and third materialsare different. The monolayers of the second and third materials can forma nanolaminate material. At least about 80% (e.g., at least about 90%,at least about 99%) of the volume of the trench can be filled bysequentially forming the plurality of monolayers of the second materialwithin the trench. The second material can be different from the firstmaterial. The layer of the first material and the second material canform a continuous layer. The continuous layer can be birefringent forlight of wavelength λ propagating through the continuous layer along anaxis, wherein λ is between 150 nm and 2,000 nm. The article can includeadditional trenches formed in the surface of the layer of the firstmaterial. The method can further include filling at least about 50% of avolume of each of the additional trenches by sequentially forming aplurality of monolayers of the second material within the additionaltrenches. The method can further include filling at least about 80%(e.g., at least about 90%, at least about 99%) of a volume of each ofthe additional trenches by sequentially forming a plurality ofmonolayers of the second material within the additional trenches. Thetrenches can be separated by rows of the first material. The layer ofthe first material can form a surface relief grating. The surface reliefgrating can have a grating period of about 500 nm or less (e.g., about400 nm or less, about 300 mm or less, about 200 nm or less, about 100 nmor less).

The trench can be formed by etching (e.g., reactive ion etching) acontinuous layer of the first material. The trench can be formedlithographically. For example, the trench can be formed usingnano-imprint lithography or holographic lithography. Where the trench isformed using nano-imprint lithography, the nano-imprint lithography caninclude forming a pattern in a thermoplastic material. Alternatively, oradditionally, the nano-imprint lithography can include forming a patternin a UV curable material.

The method can further include forming a layer of the second materialover the filled trench by sequentially forming monolayers of the secondmaterial over the trench. The layer of the second material has a surfacewith an arithmetic mean roughness of about 50 nm or less (e.g., about 40nm or less, about 30 nm or less, about 20 mm or less, about 10 nm orless).

The second material can be a dielectric material. In some embodiments,forming the plurality of monolayers of the second material comprisesdepositing a monolayer of a precursor and exposing the monolayer of theprecursor to a reagent to provide a monolayer of the second material.The reagent can chemically react with the precursor to form the secondmaterial. For example, the reagent can oxidize the precursor to form thesecond material. Depositing the monolayer of the precursor can includeintroducing a first gas comprising the precursor into a chamber housingthe article. A pressure of the first gas in the chamber can be about0.01 to about 100 Torr while the monolayer of the precursor isdeposited. Exposing the monolayer of the precursor to the reagent caninclude introducing a second gas comprising the reagent into thechamber. A pressure of the second gas in the chamber can be about 0.01to about 100 Torr while the monolayer of the precursor is exposed to thereagent. A third gas can be introduced into the chamber after the firstgas is introduced and prior to introducing the second gas. The third gascan be inert with respect to the precursor. The third gas can include atleast one gas selected from the group consisting of helium, argon,nitrogen, neon, krypton, and xenon. The precursor can be selected fromthe group consisting of tris(tert-butoxy)silanol, (CH₃)₃Al, TiCl₄,SiCl₄, SiH₂Cl₂, TaCl₃, AlCl₃, Hf-ethaoxide and Ta-ethaoxide.

The trench can have a width of about 1,000 nm or less (e.g., about 900mm or less, about 800 mm or less, about 700 nm or less, about 600 nm orless, about 500 m or less, about 400 mm or less, about 300 nm or less,about 200 nm or less). The trench can have a depth of about 10 nm ormore (e.g., about 20 nm or more, about 30 m or more, about 40 nm ormore, about 50 nm or more, about 75 m or more, about 100 mm or more,about 150 nm or more, about 200 nm or more, about 300 mm or more, about400 nm or more, about 500 nm or more, about 1,000 or more, about 1,500nm or more, about 2,000 or more).

The method can further include forming a second birefringent layer onthe layer of the first material after filling the trench. The secondbirefringent layer can include a plurality of trenches and forming thesecond birefringent layer includes filling the plurality of trenches bysequentially forming a plurality of monolayers of a third materialwithin the trenches of the second birefringent layer. The method canalso include forming additional birefringent layers on the secondbirefringent layer.

In certain embodiments, the grating can be a surface relief grating. Thegrating can have a grating period of about 2,000 nm or less (e.g., about1,500 nm or less, about 1,000 or less, about 750 nm or less, about 500nm or less, about 300 nm or less, about 200 nm or less).

The optical retardation film can be form birefringent.

The article can further include at least one antireflection film,wherein a surface of the article comprises a surface of theantireflection film. In some embodiments, the article also includes alayer of a third material adjacent the continuous layer. The article caninclude a layer of the nanolaminate material adjacent the continuouslayer. The layer of the nanolaminate material adjacent the continuouslayer can have a surface with an arithmetic mean roughness of about 50nm or less (e.g., about 40 nm or less, about 30 nm or less, about 20 nmor less, about 10 nm or less). The nanolaminate material can have arefractive index of about 1.3 or more at λ (e.g., about 1.4 or more,about 1.5 or more, about 1.6 or more, about 1.7 or more, about 1.8 ormore, about 1.9 or more, about 2.0 or more, about 2.1 or more). Thefirst material can have a refractive index of about 1.3 or more at λ(e.g., about 1.4 or more, about 1.5 or more, about 1.6 or more, about1.7 or more, about 1.8 or more, about 1.9 or more, about 2.0 or more,about 2.1 or more). The nanolaminate material can include portions of asecond material and portions of a third material, wherein the second andthird materials are different. In some embodiments, the first and thirdmaterials are the same.

The nanolaminate material can include a dielectric material, aninorganic material, and/or a metal. The nanolaminate material caninclude a material selected from a group consisting of SiO₂, SiN_(x),Si, Al₂O₃, ZrO₂, Ta₂O₅, TiO₂, HfO₂, Nb₂O₅, and MgF₂.

The first material can be a dielectric material, an inorganic material,a glass, a polymer, a semiconductor, and/or a metal. In certainembodiments, the first material is selected from a group consisting ofSiO₂, SiN_(x), Si, Al₂O₃, ZrO₂, Ta₂O₅, TiO₂, HfO₂; Nb₂O₅, and MgF₂.

The continuous layer can form a grating with a grating period of about500 nm or less (e.g., about 200 nm or less, about 100 nm or less, about50 nm or less). The rows of the first material can have a minimum widthof about 500 nm or less (about 200 nm or less, about 100 nm or less,about 50 nm or less, about 20 nm or less, about 10 nm or less). The rowsof the first material can have a minimum width that is the same ordifferent than a minimum width of the rows of the nanolaminate material.A minimum width of each of the rows of the first material can besubstantially the same. Alternatively, or additionally, a minimum widthof each of the rows of the nanolaminate material is substantially thesame.

The continuous layer has a thickness of about 15 nm or more (e.g., about30 nm or more, about 50 nm or more, about 75 nm or more, about 100 nm ormore, about 150 or more, about 200 nm or more, about 300 nm or more,about 500 nm or more, about 1,000 nm or more, about 1,500 nm or more,about 2,000 or more). In certain embodiments, the continuous layer hasan optical retardation of about 1 nm or more (e.g., about 2 nm or more,about 5 nm or more, about 10 nm or more, about 20 nm or more, about 50nm or more) for light of wavelength λ propagating through the continuouslayer along an axis, wherein λ is between 150 nm and 2,000 nm. Thecontinuous layer can have an optical retardation of about 2,000 nm orless for light of wavelength λ propagating through the composite layeralong an axis, wherein λ is between 200 nm and 2,000 nm. In someembodiments, λ is between about 400 nm and about 700 m (e.g., betweenabout 510 nm and about 570 nm). In some embodiments, the continuouslayer has an optical retardation of about 4 nm or more for light ofwavelength λ propagating through the continuous layer along an axis,wherein λ is between about 400 nm and about 700 nm.

The article can include a second continuous layer including rows of athird material alternating with rows of a second nanolaminate material,wherein the second continuous layer is birefringent for light ofwavelength λ propagating through the second continuous layer along theaxis. The article can further include additional form the portion(s),thereby controlling the birefringence. As an example, one or moreportions of the layer can be formed from a nanolaminate. The refractiveindex of the nanolaminate can be tuned by selecting the proportion oftwo or more different materials in the nanolaminate, which can becontrolled on a monolayer by monolayer basis where the nanolaminate isformed using atomic layer deposition.

Alternatively, or additionally, precisely controlling the structure ofthe layer can accurately control the birefringence of a formbirefringent layer. For example, using lithographic techniques (e.g.,electron beam lithography, nanoimprint lithography, holographiclithography) to define the structure (e.g., depth, width and profile ofa grating) of a form birefringent layer can allow for precise control ofthe structure.

In certain embodiments, the retardance of optical retarders can beprecisely controlled. For example, the birefringence and/or depth of aform birefringent layer in an optical retarder can be preciselycontrolled to provide a desired retardance. As an example, opticalretarders can include one or more layers to control the thickness ofportions of a form birefringent layer in the retarder, such as one ormore etch stop layers.

In some embodiments, optical retarders have high transmission atwavelengths of interest. For example, optical retarders can include oneor more antireflection films on one or more interfaces that reducereflection of light at wavelengths of interest. Alternatively, oradditionally, layers of optical retarders can be formed from materialswith relatively low absorption at wavelengths of interest.

Other features, and advantages of the invention will be apparent fromthe description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an embodiment of an optical retarder.

FIGS. 2A-2J show steps in the manufacture of the optical retarder shownin FIG. 1.

FIG. 3 is a schematic diagram of an atomic layer deposition system.

FIG. 4 is a flow chart showing steps for forming a nanolaminate usingatomic layer deposition.

FIG. 5 is a cross-sectional view of another embodiment of an opticalretarder birefringent layers, wherein each of the form birefringentlayers are birefringent for light of wavelength λ propagating througheach form birefringent layer along the axis.

Embodiments of the invention may include one or more of the followingadvantages.

In some embodiments, the article can be a relatively robust opticalretarder, that can have high transmission at wavelengths of interest,and that have a retardation that can be precisely controlled. Opticalretarders can include one or more form birefringent layers. Formbirefringence results from sub-wavelength structure in a medium, whichcan be achieved by arranging at least two difference materials (e.g.,optically isotropic materials) in an alternating way. Form birefringencecan result from sub-wavelength grating structures, in which a medium hasa periodic modulation in its refractive index, where the period issubstantially less than the wavelength of interest. Since the period isless than the wavelength of interest, substantially only zero-orderdiffractions occur and all higher order diffractions become evanescent(e.g., a beam at the wavelength of interest is substantially transmittedand/or reflected). While the materials composing the form birefringentmedia can be optically isotropic (i.e., having an isotropic index ofrefraction), the media itself will be optically anisotropic, giving riseto birefringence.

In some embodiments, optical retarders can include one or more formbirefringent layers that are formed of continuous material, as opposedto, for example, having trenches filled with a gas (e.g., air).Accordingly, the optical retarders can be more mechanically robust thanoptical retarders that include non-continuous layers (e.g., layers thatinclude one or more trenches filled with air).

In certain embodiments, continuous form birefringent layers can beformed having relatively high aspect ratios between the width andthickness of portions of the layers. As an example, high aspect ratiotrenches can be etched into a layer, and the trenches subsequentlyfilled using a conformal coating method (e.g., atomic layer deposition)to provide a continuous form birefringent layer having a relatively highaspect ratio.

The birefringence of optical retarders can be precisely controlled. Toachieve this, the refractive index of one or more portions of a formbirefringent layer in an optical retarder can, for example, be tuned toa desired value by controlling the composition of

FIG. 6 is a cross-sectional view of an embodiment of an optical retarderincluding multiple retardation layers.

FIG. 7 is a cross-sectional view of a polarizer incorporating an opticalretarder.

FIG. 8 is a cross-sectional view of a liquid crystal displayincorporating an optical retarder.

FIG. 9A is a scanning electron micrograph of a sub-wavelength gratingprior to trench filling.

FIG. 9B is a scanning electron micrograph of the sub-wavelength gratingshown in FIG. 9A after trench filling.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIG. 1, an embodiment of an optical retarder 100 includes aretardation layer 110 and two antireflection films 150 and 160. Opticalretarder 100 also includes a substrate 140, an etch stop layer 130, anda cap layer 120. Retardation layer 110 is in the form of a grating andincludes portions 111 having a first refractive index and portions 112having second refractive index. Retardation layer 110 is birefringentfor light of wavelength λ propagating along an axis 101, parallel to thez-axis of the Cartesian coordinate system shown in FIG. 1. In general, λis between about 150 nm and about 5,000 nm. In certain embodiments, λcorresponds to a wavelength within the visible portion of theelectromagnetic spectrum (e.g., from about 400 nm to about 700 nm).

Portions 111 and 112 extend along the y-direction, forming a periodicstructure consisting of a series of alternating rows having differentindices of refraction. The rows corresponding to portions 111 have awidth Λ₁₁₁ in the x-direction, while the rows corresponding to portions112 have a width Λ₁₁₂ in the x-direction. The widths of the rows aresmaller than λ, resulting in retardation layer 110 being formbirefringent for light of wavelength λ without encountering significanthigh-order diffraction. Optical waves with different polarization statespropagate through retardation layer 110 with different phase shifts,which depend on the thickness of retardation layer 110, the index ofrefraction of portions 111 and 112, and Λ₁₁₁ and Λ₁₁₂. Accordingly,these parameters can be selected to provide a desired amount ofretardation to polarized light at λ.

Retardation layer 110 has a birefringence, Δn, which corresponds ton_(e)-n_(o), where n_(e), and n_(o) are the effective extraordinary andordinary indices of refraction for layer 110, respectively. Forretardation layer 110, n_(e) and n_(o) are given by: $\begin{matrix}{{n_{o}^{2} = {{\frac{\Lambda_{111}}{\Lambda_{111} + \Lambda_{112}}n_{111}^{2}} + {\frac{\Lambda_{112}}{\Lambda_{111} + \Lambda_{112}}n_{112}^{2}}}}{\frac{1}{n_{e}^{2}} = {{\frac{\Lambda_{111}}{\Lambda_{111} + \Lambda_{112}}\frac{1}{n_{111}^{2}}} + {\frac{\Lambda_{112}}{\Lambda_{111} + \Lambda_{112}}{\frac{1}{n_{112}^{2}}.}}}}} & (1)\end{matrix}$In Eq. (1), n₁₁₁ and n₁₁₂ and Λ₁₁₁ and Λ₁₁₂ refer to the refractiveindices and thickness (along the x-direction) of portions 111 and 112respectively. In general, the values of ne and n₀ depend on n₁₁₁, n₁₁₂,Λ₁₁₁ and Λ₁₁₂, and are between n₁₁₁ and n₁₁₂. Λ₁₁₁ and Λ₁₁₂ can beselected to provide a desired value of Δn based on the values for n_(e)and n_(o) given by Eq. (1). Moreover, the refractive indices n₁₁₁ andn₁₁₂, which depend on the respective compositions of portions 111 and112, can be selected to provide a desired value of Δn. In someembodiments, Δn is relatively large (e.g., about 0.1 or more, about 0.15or more, about 0.2 or more, about 0.3 or more, about 0.5 or more, about1.0 or more, about 1.5 or more, about 2.0 or more). Alternatively, inother embodiments, Δn is relatively small (e.g., about 0.05 or less,about 0.04 or less, about 0.03 or less, about 0.02 or less, about 0.01or less, about 0.005 or less, about 0.002 or less, 0.001 or less).

In general, the refractive index of portions 111 can be about 1.3 ormore (e.g., about 1.4 or more, about 1.5 or more, about 1.6 or more,about 1.7 or more, about 1.8 or more, about 1.9 or more, about 2.0 ormore, about 2.1 or more, about 2.2 or more). Furthermore, in general,the refractive index of portions 112 can be about 1.3 or more (e.g.,about 1.4 or more, about 1.5 or more, about 1.6 or more, about 1.7 ormore, about 1.8 or more, about 1.9 or more, about 2.0 or more, about 2.1or more, about 2.2 or more).

In general, Λ₁₁₁ can be about 0.2 λ or less (e.g., about 0.1 λ or less,about 0.05 λ or less, about 0.04 λ or less, about 0.03 λ or less, about0.02 λ or less, 0.01 λ or less). For example, in some embodiments, Λ₁₁₁is about 200 nm or less (e.g., about 150 nm or less, about 100 nm orless, about 80 nm or less, about 70 nm or less, about 60 nm or less,about 50 nm or less, about 40 m or less, about 30 nm or less).Similarly, Λ₁₁₂ can be about 0.2 λ or less (e.g., about 0.1 λ or less,about 0.05 λ or less, about 0.04 λ or less, about 0.03 λ or less, about0.02 λ or less, 0.01 λ or less). For example, in some embodiments, Λ₁₁₂is about 200 nm or less (e.g., about 150 nm or less, about 100 nm orless, about 80 nm or less, about 70 nm or less, about 60 nm or less,about 50 nm or less, about 40 nm or less, about 30 m or less). Λ₁₁₁ andΛ₁₁₂ can be the same as each other or different.

Along the x-axis, the refractive index of retardation layer 110 isperiodic, with a period, Λ, corresponding to Λ₁₁₁+Λ₁₁₂. In general, Λ isless than λ, such as about 0.5 λ or less (e.g., about 0.3 λ or less,about 0.2 λ or less, about 0.1 λ or less, about 0.08 λ or less, about0.05 λ or less, about 0.04 λ or less, about 0.03 λ or less, about 0.02 λor less, 0.01 λ or less). In some embodiments, Λ is about 500 nm or less(e.g., about 300 nm or less, about 200 m or less, about 100 nm or less,about 80 nm or less, about 60 m or less, about 50 nm or less, about 40nm or less).

While retardation layer 110 is shown as having 19 portions, in general,the number of portions in a retardation layer may vary as desired. Thenumber of portions depends on the period, A, and the area required bythe retarder's end use application. In some embodiments, retardationlayer 110 can have about 50 or more portions (e.g., about 100 or moreportions, about 500 or more portions, about 1,000 or more portions,about 5,000 or more portions, about 10,000 or more portions, about50,000 or more portions, about 100,000 or more portions, about 500,000more portions).

The thickness, d, of retardation layer 110 measured along the z-axis canvary as desired. In general, the thickness of layer 110 is selectedbased on the refractive indices of portions 111 and 112 and the desiredretardation of retardation layer 110 at λ. In some embodiments, d can beabout 50 nm or more (e.g., about 75 nm or more, about 100 nm or more,about 125 nm or more, about 150 nm or more, about 200 nm or more, about250 nm or more, about 300 nm or more, about 400 m or more, about 500 nmor more, about 1,000 or more, such as about 2,000 nm).

The aspect ratio of retardation layer thickness, d, to Λ₁₁₁ and/or d toΛ₁₁₂ can be relatively high. For example d:Λ₁₁₁ and/or d:Λ₁₁₂ can beabout 2:1 or more (e.g., about 3:1 or more, about 4:1 or more, about 5:1or more, about 8:1 or more, about 10:1 or more).

The retardation of retardation layer 110 corresponds to the product ofthe thickness of retardation layer 110, d, and Δn. By selectingappropriate values for Δn and the layers thickness, the retardation canvary as desired. In some embodiments, the retardation of retardationlayer 110 is about 50 nm or more (e.g., about 75 nm or more, about 100nm or more, about 125 nm or more, about 150 nm or more, about 200 nm ormore, about 250 nm or more, about 300 nm or more, about 400 nm or more,about 500 nm or more, about 1,000 or more, such as about 2,000 nm).Alternatively, in other embodiments, the retardation is about 40 nm orless (e.g., about 30 nm or less, about 20 nm or less, about 10 nm orless, about 5 m or less, about 2 nm or less). In some embodiments, theretardation corresponds to λ/4 or λ/2.

Retardation can also be expressed as a phase retardation, Γ, where$\begin{matrix}{\Gamma = {\frac{2\pi}{\lambda}\Delta\quad{{nd}.}}} & (2)\end{matrix}$For example, quarter wave retardation corresponds to Γ=π/2, while halfwave retardation corresponds to Γ=π. In general, phase retardation mayvary as desired. In some embodiments, phase retardation may be about 2πor less (e.g., about 0.8 π or less, about 0.7π or less, about 0.6π orless, about 0.5π or less, about 0.4π or less, about 0.2π or less, 0.2πor less, about 0.1π or less, about 0.05π or less, 0.1π or less).Alternatively, in other embodiments, phase retardation of retardationlayer 110 can be more than 2 π (e.g., about 3π or more, about 4π ormore, about 5π or more).

In general, the composition of portions 111 and 112 can vary as desired.Portions 111 and/or 112 can include inorganic and/or organic materials.Examples of inorganic materials include metals, semiconductors, andinorganic dielectric materials (e.g., glass). Examples of organicmaterials include polymers.

In some embodiments, portions 111 and/or portions 112 include one ormore dielectric materials, such as dielectric oxides (e.g., metaloxides), fluorides (e.g., metal fluorides), sulphides, and/or nitrides(e.g., metal nitrides). Examples of oxides include SiO₂, Al₂O₃, Nb₂O₅,TiO₂, ZrO₂, HfO₂, SnO₂, ZnO, ErO₂, Sc₂O₃, and Ta₂O₅. Examples offluorides include MgF₂. Other examples include ZnS, SiN_(x),SiO_(y)N_(x), AlN, TiN, and HfN.

The compositions of portions 111 and 112 are typically selected based ontheir optical properties and their compatibility with the processes usedto manufacture optical retarder 100 and their compatibility with thematerials used to form other layers of optical retarder 100. Thecomposition of portions 111 and/or portions 112 can be selected to haveparticular refractive indices at λ. In general, the refractive index ofportion 111 is different from the refractive index or portion 112 at λ.In some embodiments, portions 111 or portions 112 are formed from amaterial that has a relatively high index of refraction, such as TiO₂,which has a refractive index of about 2.35 at 632 nm, or Ta₂O₅, whichhas a refractive index of 2.15 at 632 nm. Alternatively, portions 111 orportions 112 can be formed from a material that has a relatively lowindex of refraction. Examples of low index materials include SiO₂ andAl₂O₃, which have refractive indices of 1.45 and 1.65 at 632 nm,respectively.

In some embodiments, the composition of portions 111 and/or portions 112have a relatively low absorption at λ, so that retardation layer 110 hasa relatively low absorption at λ. For example, retardation layer 110 canabsorb about 5% or less of radiation at λ propagating along axis 101(e.g., about 3% or less, about 2% or less, about 1% or less, about 0.5%or less, about 0.2% or less, about 0.1% or less).

Portions 111 and/or portions 112 can be formed from a single material orfrom multiple different materials. In some embodiments, one or both ofportions 111 and 112 are formed from a nanolaminate material, whichrefers to materials that are composed of layers of at least twodifferent materials and the layers of at least one of the materials areextremely thin (e.g., between one and about 10 monolayers thick).Optically, nanolaminate materials have a locally homogeneous index ofrefraction that depends on the refractive index of its constituentmaterials. Varying the amount of each constituent material can vary therefractive index of a nanolaminate. Examples of nanolaminate portionsinclude portions composed of SiO₂ monolayers and TiO₂ monolayers, SiO₂monolayers and Ta₂O₅ monolayers, or Al₂O₃ monolayers and TiO₂ monolayers.

Portions 111 and/or portions 112 can include crystalline,semi-crystalline, and/or amorphous portions. Typically, an amorphousmaterial is optically isotropic and may transmit light better thanportions that are partially or mostly crystalline. As an example, insome embodiments, both portions 111 and 112 are formed from amorphousmaterials, such as amorphous dielectric materials (e.g., amorphous TiO₂or SiO₂). Alternatively, in certain embodiments, portions 111 are formedfrom a crystalline or semi-crystalline material (e.g., crystalline orsemi-crystalline Si), while portions 112 are formed from an amorphousmaterial (e.g., an amorphous dielectric material, such as TiO₂ or SiO₂).

Referring now to other layers in optical retarder 100, in general,substrate 140 provides mechanical support to optical retarder 100. Incertain embodiments, substrate 140 is transparent to light at wavelengthλ, transmitting substantially all light impinging thereon at wavelengthλ (e.g., about 90% or more, about 95% or more, about 97% or more, about99% or more, about 99.5% or more).

In general, substrate 140 can be formed from any material compatiblewith the manufacturing processes used to produce retarder 100 that cansupport the other layers. In certain embodiments, substrate 140 isformed from a glass, such as BK7 (available from Abrisa Corporation),borosilicate glass (e.g., pyrex available from Corning), aluminosilicateglass (e.g., C1737 available from Corning), or quartz/fused silica. Insome embodiments, substrate 140 can be formed from a crystallinematerial, such as a non-linear optical crystal (e.g., LiNbO₃ or amagneto-optical rotator, such as garnett) or a crystalline (orsemicrystalline) semiconductor (e.g., Si, InP, or GaAs). Substrate 140can also be formed from an inorganic material, such as a polymer (e.g.,a plastic).

Etch stop layer 130 is formed from a material resistant to etchingprocesses used to etch the material(s) from which portions 112 areformed (see discussion below). The material(s) forming etch stop layer130 should also be compatible with substrate 140 and with the materialsforming retardation layer 110. Examples of materials that can form etchstop layer 130 include HfO₂, SiO₂, Ta₂O₅, TiO₂, SiN_(x), or metals(e.g., Cr, Ti, Ni).

The thickness of etch stop layer 130 can be varied as desired.Typically, etch stop layer 130 is sufficiently thick to preventsignificant etching of substrate 140, but should not be so thick as toadversely impact the optical performance of optical retarder 100. Insome embodiments, etch stop layer is about 500 nm or less (e.g., about250 nm or less, about 100 nm or less, about 75 nm or less, about 50 nmor less, about 40 nm or less, about 30 nm or less, about 20 nm or less).

Cap layer 120 is typically formed from the same material(s) as portions111 of retardation layer 110 and provides a surface 121 onto whichadditional layers, such as the layers forming antireflection film 150,can be deposited. Surface 121 can be substantially planar.

Antireflection films 150 and 160 can reduce the reflectance of light ofwavelength λ impinging on and exiting optical retarder 100.Antireflection film 150 and 160 generally include one or more layers ofdifferent refractive index. As an example, one or both of antireflectionfilms 150 and 160 can be formed from four alternating high and low indexlayers. The high index layers can be formed from TiO₂ or Ta₂O₅ and thelow index layers can be formed from SiO₂ or MgF₂. The antireflectionfilms can be broadband antireflection films or narrowband antireflectionfilms.

In some embodiments, optical retarder 100 has a reflectance of about 5%or less of light impinging thereon at wavelength λ (e.g., about 3% orless, about 2% or less, about 1% or less, about 0.5% or less, about 0.2%or less). Furthermore, optical retarder 100 can have high transmissionof light of wavelength λ. For example, optical retarder can transmitabout 95% or more of light impinging thereon at wavelength λ (e.g.,about 98% or more, about 99% or more, about 99.5% or more).

In general, optical retarder 100 can be prepared as desired. FIGS. 2A-2Jshow different phases of an example of a preparation process. Initially,substrate 140 is provided, as shown in FIG. 2A. Surface 141 of substrate140 can be polished and/or cleaned (e.g., by exposing the substrate toone or more solvents, acids, and/or baking the substrate).

Referring to FIG. 2B, etch stop layer 130 is deposited on surface 141 ofsubstrate 140. The material forming etch stop layer 130 can be formedusing one of a variety of techniques, including sputtering (e.g., radiofrequency sputtering), evaporating (e.g., electron beam evaporation, ionassisted deposition (LAD) electron beam evaporation), or chemical vapordeposition (CVD) such as plasma enhanced CVD (PECVD), ALD, or byoxidization. As an example, a layer of HfO₂ can be deposited onsubstrate 140 by _IAD electron beam evaporation.

Referring to FIG. 2C, an intermediate layer 210 is then deposited onsurface 131 of etch stop layer 130. Portions 112 are etched fromintermediate layer 210, so intermediation layer 210 is formed from thematerial used for portions 112. The material forming intermediate layer210 can be deposited using one of a variety of techniques, includingsputtering (e.g., radio frequency sputtering), evaporating (e.g.,election beam evaporation), or chemical vapor deposition (CVD) (e.g.,plasma enhanced CVD). As an example, a layer of SiO₂ can be deposited onetch stop layer 130 by sputtering (e.g., radio frequency sputtering),CVD (e.g., plasma enhanced CVD), or electron beam evaporation (e.g., LADelectron beam deposition). The thickness of intermediate layer 210 isselected based on the desired thickness of retardation layer 110.

Intermediate layer 210 is processed to provide portions 112 ofretardation layer 110 using lithographic techniques. For example,portions 112 can be formed from intermediate layer 210 using electronbeam lithography or photolithograpy (e.g., using a photomask or usingholographic techniques). In some embodiments, portions 112 are formedusing nano-imprint lithography. Referring to FIG. 2D, nano-imprintlithography includes forming a layer 220 of a resist on surface 211 ofintermediate layer 210. The resist can be polymethylmethacrylate (PMMA)or polystyrene (PS), for example. Referring to FIG. 2E, a pattern isimpressed into resist layer 220 using a mold. The patterned resist layer220 includes thin portions 221 and thick portions 222. Patterned resistlayer 220 is then etched (e.g., by oxygen reactive ion etching (RIE)),removing thin portions 221 to expose portions 224 of surface 211 ofintermediate layer 210, as shown in FIG. 2F. Thick portions 222 are alsoetched, but are not completely removed. Accordingly, portions 223 ofresist remain on surface 211 after etching.

Referring to FIG. 2G, the exposed portions of intermediate layer 210 aresubsequently etched, forming trenches 212 in intermediate layer 210. Theunetched portions of intermediate layer 210 correspond to portions 112of retardation layer 110. Intermediate layer 210 can be etched using,for example, reactive ion etching, ion beam etching, sputtering etching,chemical assisted ion beam etching (CAIBE), or wet etching. The exposedportions of intermediate layer 210 are etched down to etch stop layer130, which is formed from a material resistant to the etching method.Accordingly, the depth of trenches 212 formed by etching is the same asthe thickness of portions 112. After etching trenches 212, residualresist 223 is removed from portions 112. Resist can be removed byrinsing the article in a solvent (e.g., an organic solvent, such asacetone or alcohol), by O₂ plasma ashing, O₂ RIE, or ozone cleaning.

Referring to FIG. 2I, after removing residual resist, material isdeposited onto the article, filling trenches 212 and forming cap layer120. The filled trenches correspond to portions 111 of retardation layer110. Material can be deposited onto the article in a variety of ways,including sputtering, electron beam evaporation, CVD (e.g., high densityCVD) or atomic layer deposition (ALD). Note that where cap layer 120 isformed and trenches 212 are filled during the same deposition step,portions 111 and cap layer 120 are formed from a continuous portion ofmaterial.

Finally, antireflection films 150 and 160 are deposited onto surface 121of cap layer 120 and surface 142 of substrate 140, respectively:Materials forming the antireflection films can be deposited onto thearticle by sputtering, electron beam evaporation, or ALD, for example.

As mentioned previously, in some embodiments, portions 111 ofretardation layer 110, cap layer 120, and/or one or both ofantireflection films 150 and 160 are prepared using atomic layerdeposition (ALD). For example, referring to FIG. 3, an ALD system 300 isused to fill trenches 212 of an intermediate article 301 (composed ofsubstrate 140, cap layer 130, and portions 112) with a nanolaminatemultilayer film, forming portions 111 and cap layer 120. Deposition ofthe nanolaminate multilayer film occurs monolayer by monolayer,providing substantial control over the composition and thickness of thefilms. During deposition of a monolayer, vapors of a precursor areintroduced into the chamber and are adsorbed onto exposed surfaces ofportions 112, etch stop layer surface 131 or previously depositedmonolayers adjacent these surfaces. Subsequently, a reactant isintroduced into the chamber that reacts chemically with the adsorbedprecursor, forming a monolayer of a desired material. The self-limitingnature of the chemical reaction on the surface can provide precisecontrol of film thickness and large-area uniformity of the depositedlayer. Moreover, the non-directional adsorption of precursor onto eachexposed surface provides for uniform deposition of material onto theexposed surfaces, regardless of the orientation of the surface relativeto chamber 110. Accordingly, the layers of the nanolaminate film conformto the shape of the trenches of intermediate article 301.

ALD system 300 includes a reaction chamber 310, which is connected tosources 350, 360, 370, 380, and 390 via a manifold 330. Sources 350,360, 370, 380, and 390 are connected to manifold 330 via supply lines351, 361, 371, 381, and 391, respectively. Valves 352, 362, 372, 382,and 392 regulate the flow of gases from sources 350, 360, 370, 380, and390, respectively. Sources 350 and 380 contain a first and secondprecursor, respectively, while sources 360 and 390 include a firstreagent and second reagent, respectively. Source 370 contains a carriergas, which is constantly flowed through chamber 310 during thedeposition process transporting precursors and reagents to article 301,while transporting reaction byproducts away from the substrate.Precursors and reagents are introduced into chamber 310 by mixing withthe carrier gas in manifold 330. Gases are exhausted from chamber 310via an exit port 345. A pump 340 exhausts gases from chamber 310 via anexit port 345. Pump 340 is connected to exit port 345 via a tube 346.

ALD system 300 includes a temperature controller 395, which controls thetemperature of chamber 310. During deposition, temperature controller395 elevates the temperature of article 301 above room temperature. Ingeneral, the temperature should be sufficiently high to facilitate arapid reaction between precursors and reagents, but should not damagethe substrate. In some embodiments, the temperature of article 301 canbe about 500° C. or less (e.g., about 400° C. or less, about 300° C. orless, about 200° C. or less, about 150° C. or less, about 125° C. orless, about 100° C. or less).

Typically, the temperature should not vary significantly betweendifferent portions of article 301. Large temperature variations cancause variations in the reaction rate between the precursors andreagents at different portions of the substrate, which can causevariations in the thickness and/or morphology of the deposited layers.In some embodiments, the temperature between different portions of thedeposition surfaces can vary by about 40° C. or less (e.g., about 30° C.or less, about 20° C. or less, about 10° C. or less, about 5° C. orless).

Deposition process parameters are controlled and synchronized by anelectronic controller 399. Electronic controller 399 is in communicationwith temperature controller 395; pump 340; and valves 352, 362, 372,382, and 392. Electronic controller 399 also includes a user interface,from which an operator can set deposition process parameters, monitorthe deposition process, and otherwise interact with system 300.

Referring to FIG. 4, the ALD process is started (410) when system 300introduces the first precursor from source 350 into chamber 310 bymixing it with carrier gas from source 370 (420). A monolayer of thefirst precursor is adsorbed onto exposed surfaces of article 301, andresidual precursor is purged from chamber 310 by the continuous flow ofcarrier gas through the chamber (430). Next, the system introduces afirst reagent from source 360 into chamber 310 via manifold 330 (440).The first reagent reacts with the monolayer of the first precursor,forming a monolayer of the first material. As for the first precursor,the flow of carrier gas purges residual reagent from the chamber (450).Steps 420 through 460 are repeated until the layer of the first materialreaches a desired thickness (460).

In embodiments where the films are a single layer of material, theprocess ceases once the layer of first material reaches the desiredthickness (470). However, for a nanolaminate film, the system introducesa second precursor into chamber 310 through manifold 330 (380). Amonolayer of the second precursor is adsorbed onto the exposed surfacesof the deposited layer of first material and carrier gas purges thechamber of residual precursor (490). The system then introduces thesecond reagent from source 380 into chamber 310 via manifold 330. Thesecond reagent reacts with the monolayer of the second precursor,forming a monolayer of the second material (500). Flow of carrier gasthrough the chamber purges residual reagent (510). Steps 580 through 510are repeated until the layer of the second material reaches a desiredthickness (520).

Additional layers of the first and second materials are deposited byrepeating steps 520 through 530. Once the desired number of layers areformed (e.g., the trenches are filled and/or cap layer has a desiredthickness), the process terminates (540), and the coated article isremoved from chamber 310.

Although the precursor is introduced into the chamber before the reagentduring each cycle in the process described above, in other examples thereagent can be introduced before the precursor. The order in which theprecursor and reagent are introduced can be selected based on theirinteractions with the exposed surfaces. For example, where the bondingenergy between the precursor and the surface is higher than the bondingenergy between the reagent and the surface, the precursor can beintroduced before the reagent. Alternatively, if the binding energy ofthe reagent is higher, the reagent can be introduced before theprecursor.

The thickness of each monolayer generally depends on a number offactors. For example, the thickness of each monolayer can depend on thetype of material being deposited. Materials composed of larger moleculesmay result in thicker monolayers compared to materials composed ofsmaller molecules.

The temperature of the article can also affect the monolayer thickness.For example, for some precursors, a higher temperate can reduceadsorption of a precursor onto a surface during a deposition cycle,resulting in a thinner monolayer than would be formed if the substratetemperature were lower.

The type or precursor and type of reagent, as well as the precursor andreagent dosing can also affect monolayer thickness. In some embodiments,monolayers of a material can be deposited with a particular precursor,but with different reagents, resulting in different monolayer thicknessfor each combination. Similarly, monolayers of a material formed fromdifferent precursors can result in different monolayer thickness for thedifferent precursors.

Examples of other factors which may affect monolayer thickness includepurge duration, residence time of the precursor at the coated surface,pressure in the reactor, physical geometry of the reactor, and possibleeffects from the byproducts on the deposited material. An example ofwhere the byproducts affect the film thickness are where a byproductetches the deposited material. For example, HCl is a byproduct whendepositing TiO₂ using a TiCl₄ precursor and water as a reagent. HCl canetch the deposited TiO₂ before it is exhausted. Etching will reduce thethickness of the deposited monolayer, and can result in a varyingmonolayer thickness across the substrate if certain portions of thesubstrate are exposed to HCl longer than other portions (e.g., portionsof the substrate closer to the exhaust may be exposed to byproductslonger than portions of the substrate further from the exhaust).

Typically, monolayer thickness is between about 0.1 nm and about fivenm. For example, the thickness of one or more of the depositedmonolayers can be about 0.2 nm or more (e.g., about 0.3 nm or more,about 0.5 nm or more). In some embodiments, the thickness of one or moreof the deposited monolayers can be about three nm or less (e.g., abouttwo nm, about one nm or less, about 0.8 nm or less, about 0.5 nm orless).

The average deposited monolayer thickness may be determined bydepositing a preset number of monolayers on a substrate to provide alayer of a material. Subsequently, the thickness of the deposited layeris measured (e.g., by ellipsometry, electron microscopy, or some othermethod). The average deposited monolayer thickness can then bedetermined as the measured layer thickness divided by the number ofdeposition cycles. The average deposited monolayer thickness maycorrespond to a theoretical monolayer thickness. The theoreticalmonolayer thickness refers to a characteristic dimension of a moleculecomposing the monolayer, which can be calculated from the material'sbulk density and the molecules molecular weight. For example, anestimate of the monolayer thickness for SiO₂ is ˜0.37 nm. The thicknessis estimated as the cube root of a formula unit of amorphous SiO₂ withdensity of 2.0 grams per cubic centimeter.

In some embodiments, average deposited monolayer thickness cancorrespond to a fraction of a theoretical monolayer thickness (e.g.,about 0.2 of the theoretical monolayer thickness, about 0.3 of thetheoretical monolayer thickness, about 0.4 of the theoretical monolayerthickness, about 0.5 of the theoretical monolayer thickness, about 0.6of the theoretical monolayer thickness, about 0.7 of the theoreticalmonolayer thickness, about 0.8 of the theoretical monolayer thickness,about 0.9 of the theoretical monolayer thickness). Alternatively, theaverage deposited monolayer thickness can correspond to more than onetheoretical monolayer thickness up to about 30 times the theoreticalmonolayer thickness (e.g., about twice or more than the theoreticalmonolayer thickness, about three time or more than the theoreticalmonolayer thickness, about five times or more than the theoreticalmonolayer thickness, about eight times or more than the theoreticalmonolayer thickness, about 10 times or more than the theoreticalmonolayer thickness, about 20 times or more than the theoreticalmonolayer thickness).

During the deposition process, the pressure in chamber 310 can bemaintained at substantially constant pressure, or can vary. Controllingthe flow rate of carrier gas through the chamber generally controls thepressure. In general, the pressure should be sufficiently high to allowthe precursor to saturate the surface with chemisorbed species, thereagent to react completely with the surface species left by theprecursor and leave behind reactive sites for the next cycle of theprecursor. If the chamber pressure is too low, which may occur if thedosing of precursor and/or reagent is too low, and/or if the pump rateis too high, the surfaces may not be saturated by the precursors and thereactions may not be self limited. This can result in an uneventhickness in the deposited layers. Furthermore, the chamber pressureshould not be so high as to hinder the removal of the reaction productsgenerated by the reaction of the precursor and reagent. Residualbyproducts may interfere with the saturation of the surface when thenext dose of precursor is introduced into the chamber. In someembodiments, the chamber pressure is maintained between about 0.01 Torrand about 100 Torr (e.g., between about 0.1 Torr and about 20 Torr,between about 0.5 Torr and 10 Torr, such as about 1 Torr).

Generally, the amount of precursor and/or reagent introduced during eachcycle can be selected according to the size of the chamber, the area ofthe exposed substrate surfaces, and/or the chamber pressure. The amountof precursor and/or reagent introduced during each cycle can bedetermined empirically.

The amount of precursor and/or reagent introduced during each cycle canbe controlled by the timing of the opening and closing of valves 352,362, 382, and 392. The amount of precursor or reagent introducedcorresponds to the amount of time each valve is open each cycle. Thevalves should open for sufficiently long to introduce enough precursorto provide adequate monolayer coverage of the substrate surfaces.Similarly, the amount of reagent introduced during each cycle should besufficient to react with substantially all precursor deposited on theexposed surfaces. Introducing more precursor and/or reagent than isnecessary can extend the cycle time and/or waste precursor and/orreagent. In some embodiments, the precursor dose corresponds to openingthe appropriate valve for between about 0.1 seconds and about fiveseconds each cycle (e.g., about 0.2 seconds or more, about 0.3 secondsor more, about 0.4 seconds or more, about 0.5 seconds or more, about 0.6seconds or more, about 0.8 seconds or more, about one second or more).Similarly, the reagent dose can correspond to opening the appropriatevalve for between about 0.1 seconds and about five seconds each cycle(e.g., about 0.2 seconds or more, about 0.3 seconds or more, about 0.4seconds or more, about 0.5 seconds or more, about 0.6 seconds or more,about 0.8 seconds or more, about one second or more).

The time between precursor and reagent doses corresponds to the purge.The duration of each purge should be sufficiently long to removeresidual precursor or reagent from the chamber, but if it is longer thanthis it can increase the cycle time without benefit. The duration ofdifferent purges in each cycle can be the same or can vary. In someembodiments, the duration of a purge is about 0.1 seconds or more (e.g.,about 0.2 seconds or more, about 0.3 seconds or more, about 0.4 secondsor more, about 0.5 seconds or more, about 0.6 seconds or more, about 0.8seconds or more, about one second or more, about 1.5 seconds or more,about two seconds or more). Generally, the duration of a purge is about10 seconds or less (e.g., about eight seconds or less, about fiveseconds or less, about four seconds or less, about three seconds orless).

The time between introducing successive doses of precursor correspondsto the cycle time. The cycle time can be the same or different forcycles depositing monolayers of different materials. Moreover, the cycletime can be the same or different for cycles depositing monolayers ofthe same material, but using different precursors and/or differentreagents. In some embodiments, the cycle time can be about 20 seconds orless (e.g., about 15 seconds or less, about 12 seconds or less, about 10seconds or less, about 8 seconds or less, about 7 seconds or less, about6 seconds or less, about 5 seconds or less, about 4 seconds or less,about 3 seconds or less). Reducing the cycle time can reduce the time ofthe deposition process.

The precursors are generally selected to be compatible with the ALDprocess, and to provide the desired deposition materials upon reactionwith a reagent. In addition, the precursors and materials should becompatible with the material on which they are deposited (e.g., with thesubstrate material or the material forming the previously depositedlayer). Examples of precursors include chlorides (e.g., metalchlorides), such as TiCl₄, SiCl₄, SiH₂Cl₂, TaCl₃, HfCl₄, InCl₃ andAlCl₃. In some embodiments, organic compounds can be used as a precursor(e.g., Ti-ethaOxide, Ta-ethaOxide, Nb-ethaOxide). Another example of anorganic compound precursor is (CH₃)₃Al.

The reagents are also generally selected to be compatible with the ALDprocess, and are selected based on the chemistry of the precursor andmaterial. For example, where the material is an oxide, the reagent canbe an oxidizing agent. Examples of suitable oxidizing agents includewater, hydrogen peroxide, oxygen, ozone, (CH₃)₃Al, and various alcohols(e.g., Ethyl alcohol CH₃OH). Water, for example, is a suitable reagentfor oxidizing precursors such as TiCl₄ to obtain TiO₂, AlCl₃ to obtainAl₂O₃, and Ta-ethaoxide to obtain Ta₂O₅, Nb-ethaoxide to obtain Nb₂O₅,HfCl₄ to obtain HfO₂, ZrCl₄ to obtain ZrO₂, and InCl₃ to obtain In₂O₃.In each case, HCl is produced as a byproduct. In some embodiments,(CH₃)₃Al can be used to oxidize silanol to provide SiO₂.

While certain embodiments have been described, the invention, ingeneral, is not so limited. For example, while optical retarder 100 (seeFIG. 1) shows a specific configuration of different layers, otherembodiments can include additional or fewer layers. For example, incertain embodiments optical retarders need not include one or both ofantireflection films 150 and 160. In some embodiments, optical retarderscan include additional antireflection films (e.g., between substratelayer 140 and etch stop layer 130). Embodiments can also includeprotective layers, such as hardcoat layers (e.g., hardcoat polymers) onone or both of antireflection films 150 and 160. In certain embodiments,optical retarders need not include a cap layer. For example, the caplayer, which forms while filling trenches between portions 112, can beremoved once portions 111 are formed. The cap layer can be removed by,e.g., chemical mechanical polishing or etching.

Referring to FIG. 5, in some embodiments, an optical retarder 600 isformed by partially etching trenches directly into a substrate layer,and subsequently filling the trenches to provide a continuousretardation layer 610. Optical retarder 600 also includes a cap layer620, and a base layer 630, which corresponds to an unetched portion ofthe original substrate layer. An antireflection film 640 is deposited onsurface 621 of cap layer 602, and a second antireflection film 650 isdeposited on surface 631 of base layer 630.

In certain embodiments, optical retarders can be formed from more thanone retardation layer. For example, referring to FIG. 6, an opticalretarder 800 includes four retardation layers 810, 820, 830, and 840.Optical retarder 800 also includes a substrate layer 801, an etch stoplayer 805, and cap layers 811, 821, 831, and 841.

Retardation layers 810, 820, 830, and 840 can have the same retardationfor a beam of light having wavelength λ, or can have differentretardations.

Optical retarder 800 can be prepared using methods disclosed herein. Forexample, each retardation layer and its corresponding cap layer can beformed by depositing and etching an intermediate layer either on etchstop layer 805 (e.g., retardation layer 810) or on the previouslydeposited cap layer (e.g., retardation layers 820, 830, and 840), andthen depositing materials to fill the etched trenches and form the caplayers.

In some embodiments, additional etch stop layers can be deposited onto acap layer prior to forming a subsequent retardation layer. Of course,other layers may also be included, such as antireflection films, forexample.

In general, the thickness of retardation layers 810, 820, 830, and 840along the z-direction, the width of their portions (along thex-direction), and the materials used to form them may vary as desired.In some embodiments, retardation layers 810, 820, 830, and 840 areidentical, while in other embodiments, one or more of the retardationlayers can be different (e.g., composed of one or more differentmaterials to the other retardation layers, have a different thickness,and/or have a different birefringence).

Moreover, while optical retarder 800 has four retardation layers, ingeneral, embodiments can include more than or less than four retardationlayers. Optical retarders can include two retardation layers, threeretardation layers, or five or more retardation layers (e.g., about 10or more retardation layers, about 20 or more retardation layers, about30 or more retardation layers, about 100 or more retardation layers,about 1000 or more retardation layers).

The total phase retardation for light of wavelength λ propagatingthrough an optical retarder having more than one retardation layer canbe relatively large. For example, an optical retarder can have a phaseretardation of about 2π or more at λ (e.g., about 3π or more, about 4πor more, about 5π or more, about 8π or more, about 10π or more, about12π or more, about 15π or more, about 20π or more, about 30π or more.

The total thickness (along the z-direction) of optical retarders thaninclude more than one retardation layer can be about 200 μm or more(e.g., about 500 μm or more, about 800 μm or more, about 1,000 μm ormore, about 1,500 μm or more, about 2,000 μm or more, about 5,000 μm ormore).

In certain embodiments, optical retarders can be used as an opticalwalk-off crystal, which splits non-normally incident light (i.e., lightnot propagating along the z-direction) into an ordinary and anextraordinary ray, which exit the retarder along different paths. Suchoptical walk-off crystals can be re-cut and polished into a wedge.Walk-off crystals can be used in numerous applications, such as intelecom isolators, circulators, or interleavers, and/or in consumerapplications, such as optical low pass filters, for example.

Although embodiments of optical retarders have been described thatinclude form birefringent layers that have a rectangular gratingprofile, other embodiments are also possible. For example, in someembodiments, the grating profile of a form birefringent layer can becurved, such as having a sinusoidal shape. In another example, thegrating can have a triangular or sawtooth profile.

Furthermore, while the grating period in the form birefringent layers ofoptical retarders has been described as constant, in certain embodimentsthe grating period may vary. In some embodiments, portions of formbirefringent layers can be non-periodically arranged.

Optical retarders such as those described herein can be incorporatedinto optical devices, including passive optical devices (e.g.,polarizers) and active optical devices (e.g., liquid crystal displays).Optical retarders can be integrated into the device, providing amonolithic device, or can be arranged separately from other componentsof the device.

Referring to FIG. 7, an example of a passive optical deviceincorporating an optical retarder is a polarizer 660. Polarizer 660includes a polarizing film 670 and an optical retarder 680. Polarizingfilm 670 can be a sheet polarizer (e.g., iodine-stained polyvinylalcohol) or a nano-structured polarizer, such as is disclosed in U.S.patent application Ser. No. 10/644,643, entitled “MULTILAYER STRUCTURESFOR POLARIZATION AND BEAM CONTROL,” and PCT Patent Application SerialNo. PCT/US03/26024, entitled “METHOD AND SYSTEM FOR PROVIDING BEAM FORPOLARIZATION,” the contents both of which are hereby incorporated byreference in their entirety.

Polarizing film 670 linearly polarizes light incident on polarizer 660propagating along axis 661. Optical retarder 680 then retards thelinearly polarized light, providing polarized light with a desiredellipticity exiting polarizer 660. The ellipticity of the exiting lightcan vary as desired by choosing the parameters associated with theretardation layer of optical retarder 680 to provide a desired amount ofretardation. For example, the exiting light can be circularly polarizedor elliptically polarized.

Referring to FIG. 8, an example of an active optical deviceincorporating an optical retarder is a liquid crystal display 700, whichincludes a substrate 710 (e.g., a silicon substrate), a reflectiveelectrode 720, a layer 730 of a liquid crystal (e.g., a nematic orferroelectric liquid crystal), a transparent electrode 740 (e.g., formedfrom indium tin oxide), an optical retarder 750, and a polarizing film760. Optical retarder 750 retards polarized light transmitted throughpolarizing film 760. This light reflects from electrode 720, propagatingthrough liquid crystal layer 730 twice. The reflected light is againretarded by optical retarder 760 before impinging on polarizing film 760a second time. Depending on the voltage applied across electrodes 720and 740, the reflected light is either absorbed or transmitted bypolarizing film 760, corresponding to a dark or bright pixel,respectively. Optionally, LCD 700 includes color filters that absorbcertain wavelengths in the visible spectrum providing a colored image.While LCD 700 is a reflective display, the optical retarders disclosedherein can be used in other types of display, such as transmissivedisplays or transflective displays.

The following examples are illustrative and not intended as limiting.

EXAMPLES

Optical retarders were prepared as follows. A 0.5 mm thick BK7 wafer(four inches in diameter), obtained from Abrisa Corporation (SantaPaula, Calif.), was cleaned by removing insoluble organic contaminantswith a H₂O:H₂O₂:NH₄OH solution, and removing ionic and heavy metalatomic contaminants using a H₂O:H₂O₂:HCl solution. Thereafter, the waferwas rinsed with isopropyl alcohol and deionized water, and spin dried.

A sub-wavelength grating was etched into the BK7 wafer as follows. TheBK7 wafer was spin coated with a thin layer (˜180 nm) of PMMA (molecularweight of 15 K purchased from Sigma-Aldrich, St. Louis, Mo.), which wasbaked on a hot plate at about 115° C. for about one hour. After baking,the resist was imprinted with a grating mold having a period of 200 nmand depth of about 110 nm, and a grating linewidth of about 100 nm. Themold included a patterned SiO₂ layer (about 200 nm thick) on a 0.5 mmthick silicon substrate. The mold was prepared using methods disclosedby J. Wang, Z. Yu, and S. Y. Chou, in J. Vac. Sci. Technol., B17, 2957(1999). After imprinting, the deformed UV curable resist was fully curedby exposing to UV light through the BK7 substrate side. The mold wasthen separated from the resist, leaving a mask with a negative patternof the mold profile. The mask was etched by O₂ RIE until the BK7 waferwas exposed in the recessed portions of the mask. This etch wasperformed using a plasma-therm 790 (available from Unaxis, Inc., St.Petersburg, Fla.). The pressure during etching was 4 mtorr. The powerwas set to 70 W and the oxygen flow rate during the etching was 10 sccm.The total thickness of resist etched to expose the BK7 wafer was about120 nm.

After etching the mask, about 50 nm of Cr was deposited on the remainingresist/exposed BK7 wafer by e-beam evaporation at high vacuum (i.e.,less than about 5×10⁻⁶ torr) at an oblique angle from the wafer normal.The oblique angle was about 65 degrees. Cr was deposited on the top andsidewall of the remaining mask lines, providing a hard mask for etchingof BK7. After Cr deposition, O₂ RIE was used again to etch any exposedresist that was not covered by the Cr. CHF₃ RIE was then used to etchexposed portions of the BK7 wafer surface to form a subwavelengthgrating in the wafer. The BK7 was etched using a plasma-term 720. Thechamber pressure was about 5 mtorr, the power was about 100 W, and flowrate of 10 sccm and 1 sccm of CHF₃ and O₂ were used, respectively. 100nm wide trenches having a depth of about 630 m were etched into the BK7wafer. After etching the BK7, the Cr was removed by immersing the waferinto CR-7 Cr etchant (obtained from Cyantek, Fremont, Calif.) for about30 minutes. Residual resist was subsequently removed by O₂ RIE.

The trenches were filled with a nanolaminate material composed of TiO₂and SiO₂. The nanolaminate material was deposited by ALD, which wasperformed using a P-400A ALD apparatus, obtained from Planar Systems,Inc. (Beaverton, Oreg.). Prior to depositing the nanolaminate, theetched wafer was heated to 300° C. inside the ALD chamber for aboutthree hours. The chamber was flushed with nitrogen gas, flowed at about2 SLM, maintaining the chamber pressure at about 0.75 Torr. The TiO₂precursor was Ti-ethaoxide, which was heated to about 140° C. The SiO₂precursor was silanol, heated to about 110° C. For both precursors, thereagent used was water, which was maintained at about 13° C. TheTi-ethaoxide and silanol were 99.999% grade purity, obtained fromSigma-Aldrich (St. Louis, Mo.). The nanolaminate was formed by repeatinga cycle in which 10 monolayers of TiO₂ were deposited, followed by asingle monolayer of SiO₂. To deposit a TiO₂ monolayer, water wasintroduced to the chamber for two seconds, followed by a two secondnitrogen purge. Then Ti-ethaoxide was introduced to the chamber,followed by another two second nitrogen purge. SiO₂ monolayers weredeposited by introducing water to the ALD chamber for one second,followed by a two second nitrogen purge. Silanol was then introduced forone second. The chamber was then purged for three seconds with nitrogenbefore the next pulse of reagent. The refractive index of thenanolaminate was estimated to be approximately 1.88 at 632 nm, asdetermined from measurements of a nanolaminate film similarly preparedon a flat glass substrate.

The retardation of an optical retarder was measured using an M-2000V®Spectroscopic Ellipsometer (commercially available from J.A. WoollamCo., Inc., Lincoln, Nebr.) to be 23.85 nm at a wavelength of 551 nm.

Unfilled and filled gratings were studied using scanning electronmicroscopy, which was performed using a LEO thermo-emission scanningelectron microscope. To perform this study, a sample was cleaved andcoated with a thin layer of Au. The cross section of the cleavedinterface was then viewed. FIGS. 9A and 9B show SEM micrographs of agrating prior to and after trench filling, respectively.

Other embodiments are in the following claims.

1. A method, comprising: providing an article that includes a layer of afirst material, wherein the layer of the first material includes atleast one trench and wherein the layer is birefringent for light ofwavelength λ propagating through the layer along an axis, wherein λ isbetween 150 nm and 2,000 nm; and filling at least about 50% of a volumeof the trench by sequentially forming a plurality of monolayers of asecond material within the trench.
 2. The method of claim 1, wherein thefilling further comprises forming one or more monolayers of a thirdmaterial within the trench, wherein the second and third materials aredifferent.
 3. The method of claim 2, wherein the monolayers of thesecond and third materials form a nanolaminate material.
 4. The methodof claim 1, wherein at least about 80% of the volume of the trench isfilled by sequentially forming the plurality of monolayers of the secondmaterial within the trench.
 5. The method of claim 1, wherein at leastabout 90% of the volume of the trench is filled by sequentially formingthe plurality of monolayers of the second material within the trench. 6.The method of claim 1, wherein at least about 99% of the volume of thetrench is filled by sequentially forming the plurality of monolayers ofthe second material within the trench.
 7. The method of claim 1, whereinthe second material is different from the first material.
 8. The methodof claim 1, wherein the layer of the first material and the secondmaterial form a continuous layer.
 9. The method of claim 1, wherein thearticle comprises additional trenches formed in the surface of the layerof the first material.
 10. The method of claim 9, wherein the methodfurther comprises filling at least about 50% of a volume of each of theadditional trenches by sequentially forming a plurality of monolayers ofthe second material within the additional trenches.
 11. The method ofclaim 9, wherein the method further comprises filling at least about 80%of a volume of each of the additional trenches by sequentially forming aplurality of monolayers of the second material within the additionaltrenches.
 12. The method of claim 9, wherein the method furthercomprises filling at least about 90% of a volume of each of theadditional trenches by sequentially forming a plurality of monolayers ofthe second material within the additional trenches.
 13. The method ofclaim 9, wherein the method further comprises filling at least about 99%of a volume of each of the additional trenches by sequentially forming aplurality of monolayers of the second material within the additionaltrenches.
 14. The method of claim 9, wherein the trenches are separatedby rows of the first material.
 15. The method of claim 7, wherein thelayer of the first material forms a surface relief grating.
 16. Themethod of claim 15, wherein the surface relief grating has a gratingperiod of about 500 nm or less.
 17. The method of claim 7, wherein thetrench is formed by etching a continuous layer of the first material.18. The method of claim 17, wherein the etching comprising reactive ionetching.
 19. The method of claim 1, wherein the trench is formedlithographically.
 20. The method of claim 19, wherein the trench isformed using nano-imprint lithography.
 21. The method of claim 20,wherein the nano-imprint lithography includes forming a pattern in athermoplastic material.
 22. The method of claim 20, wherein thenano-imprint lithography includes forming a pattern in a UV curablematerial.
 23. The method of claim 19, wherein the trench is formed usingholographic lithography.
 24. The method of claim 1, further comprisingforming a layer of the second material over the filled trench bysequentially forming monolayers of the second material over the trench.25. The method of claim 24, wherein the layer of the second material hasa surface with an arithmetic mean roughness of about 50 nm or less. 26.The method of claim 1, wherein the second material is a dielectricmaterial.
 27. The method of claim 1, wherein forming the plurality ofmonolayers of the second material comprises depositing a monolayer of aprecursor and exposing the monolayer of the precursor to a reagent toprovide a monolayer of the second material.
 28. The method of claim 27,wherein the reagent chemically reacts with the precursor to form thesecond material.
 29. The method of claim 28, wherein the reagentoxidizes the precursor to form the second material.
 30. The method ofclaim 27, wherein depositing the monolayer of the precursor comprisesintroducing a first gas comprising the precursor into a chamber housingthe article.
 31. The method of claim 30, wherein a pressure of the firstgas in the chamber is about 0.01 to about 100 Torr while the monolayerof the precursor is deposited.
 32. The method of claim 30, whereinexposing the monolayer of the precursor to the reagent comprisesintroducing a second gas comprising the reagent into the chamber. 33.The method of claim 30, wherein a pressure of the second gas in thechamber is about 0.01 to about 100 Torr while the monolayer of theprecursor is exposed to the reagent.
 34. The method of claim 30, whereina third gas is introduced into the chamber after the first gas isintroduced and prior to introducing the second gas.
 35. The method ofclaim 27, wherein the third gas is inert with respect to the precursor.36. The method of claim 27, wherein the third gas comprises at least onegas selected from the group consisting of helium, argon, nitrogen, neon,krypton, and xenon.
 37. The method of claim 27, wherein the precursor isselected from the group consisting of tris(tert-butoxy)silanol,(CH₃)₃Al, TiCl₄, SiCl₄, SiH₂Cl₂, TaCl₃, AlCl₃, Hf-ethaoxide andTa-ethaoxide.
 38. The method of claim 1, wherein the trench has a widthof about 1,000 nm or less.
 39. The method of claim 1, wherein the trenchhas a depth of about 10 nm or more.
 40. The method of claim 8, whereinthe continuous layer is birefringent for light of wavelength λpropagating through the continuous layer along an axis, wherein λ isbetween 150 nm and 2,000 nm.
 41. A method, comprising: forming a layerof a material on a surface of a grating using atomic layer deposition.42. The method of claim 41, wherein the grating is a surface reliefgrating.
 43. The method of claim 41, wherein the grating has a gratingperiod of about 2,000 nm or less.
 44. The method of claim 1, furthercomprising forming a second birefringent layer on the layer of the firstmaterial after filling the trench.
 45. The method of claim 44, whereinthe second birefringent layer comprises a plurality of trenches andforming the second birefringent layer includes filling the plurality oftrenches by sequentially forming a plurality of monolayers of a thirdmaterial within the trenches of the second birefringent layer.
 46. Themethod of claim 44, further comprising forming additional birefringentlayers on the second birefringent layer.
 47. A method, comprising:forming an optical retardation film using atomic layer deposition. 48.The method of claim 47, wherein the optical retardation film is formbirefringent.
 49. An article, comprising: a continuous layer includingrows of a first material alternating with rows of a nanolaminatematerial, wherein the continuous layer is birefringent for light ofwavelength λ propagating through the continuous layer along an axis,wherein λ is between 150 nm and 2,000 nm.
 50. The article of claim 49,further comprising at least one antireflection film, wherein a surfaceof the article comprises a surface of the antireflection film.
 51. Thearticle of claim 49, further comprising a layer of a third materialadjacent the continuous layer.
 52. The article of claim 49, furthercomprising a layer of the nanolaminate material adjacent the continuouslayer.
 53. The article of claim 49, wherein the layer of thenanolaminate material adjacent the continuous layer has a surface withan arithmetic mean roughness of about 50 nm or less.
 54. The method ofclaim 49, wherein the layer of the nanolaminate material adjacent thecontinuous layer has a surface with an arithmetic mean roughness ofabout 20 nm or less.
 55. The method of claim 49, wherein the layer ofthe nanolaminate material adjacent the continuous layer has a surfacewith an arithmetic mean roughness of about 10 nm or less.
 56. Thearticle of claim 49, wherein the nanolaminate material has a refractiveindex of about 1.3 or more at λ.
 57. The article of claim 49, whereinthe nanolaminate material has a refractive index of about 1.5 or more atλ.
 58. The article of claim 49, wherein the nanolaminate material has arefractive index of about 1.6 or more at λ.
 59. The article of claim 49,wherein the nanolaminate material has a refractive index of about 1.7 ormore at λ.
 60. The article of claim 49, wherein the nanolaminatematerial has a refractive index of about 1.8 or more at λ.
 61. Thearticle of claim 49, wherein the nanolaminate material has a refractiveindex of about 1.9 or more at λ.
 62. The article of claim 49, whereinthe nanolaminate material has a refractive index of about 2.0 or more atλ.
 63. The article of claim 49, wherein the nanolaminate materialcomprises portions of a second material and portions of a thirdmaterial, wherein the second and third materials are different.
 64. Thearticle of claim 63, wherein the first and third materials are the same.65. The article of claim 49, wherein the nanolaminate material comprisesa dielectric material.
 66. The article of claim 49, wherein thenanolaminate material comprises an inorganic material.
 67. The articleof claim 49, wherein the nanolaminate material comprises a metal. 68.The article of claim 49, wherein the nanolaminate material comprises amaterial selected from a group consisting of SiO₂, SiN_(x), Si, Al₂O₃,ZrO₂, Ta₂O₅, TiO₂, HfO₂, Nb₂O₅, and MgF₂.
 69. The article of claim 49,wherein the first material is a dielectric material.
 70. The article ofclaim 49, wherein the first material is an inorganic material.
 71. Thearticle of claim 49, wherein the first material is a polymer.
 72. Thearticle of claim 49, wherein the first material is a semiconductor. 73.The article of claim 49, wherein the first material is a metal.
 74. Thearticle of claim 49, wherein the first material is selected from a groupconsisting of SiO₂, SiN_(x), Si, Al₂O₃, ZrO₂, Ta₂O₅, TiO₂, HfO₂, Nb₂O₅,and MgF₂.
 75. The article of claim 49, wherein the first material is aglass.
 76. The article of claim 49, wherein the continuous layer forms agrating with a grating period of about 500 nm or less.
 77. The articleof claim 49, wherein the continuous layer forms a grating with a gratingperiod of about 200 nm or less.
 78. The article of claim 49, wherein thecontinuous layer forms a grating with a grating period of about 100 nmor less.
 79. The article of claim 49, wherein the continuous layer formsa grating with a grating period of about 50 nm or less.
 80. The articleof claim 49, wherein the rows of the first material have a minimum widthof about 500 nm or less.
 81. The article of claim 49, wherein the rowsof the first material have a minimum width of about 200 nm or less. 82.The article of claim 49, wherein the rows of the first material have aminimum width of about 100 nm or less.
 83. The article of claim 49,wherein the rows of the first material have a minimum width of about 50nm or less.
 84. The article of claim 49, wherein the rows of the firstmaterial have a minimum width of about 20 nm or less.
 85. The article ofclaim 49, wherein the rows of the first material have a minimum width ofabout 10 nm or less.
 86. The article of claim 49, wherein the rows ofthe first material have a minimum width that is different than a minimumwidth of the rows of the nanolaminate material.
 87. The article of claim49, wherein the rows of the first material have a minimum width that isthe same as a minimum width of the rows of the nanolaminate material.88. The article of claim 49, wherein a minimum width of each of the rowsof the first material is substantially the same.
 89. The article ofclaim 49, wherein a minimum width of each of the rows of thenanolaminate material is substantially the same.
 90. The article ofclaim 49, wherein the continuous layer has a thickness of about 15 nm ormore.
 91. The article of claim 49, wherein the continuous layer has athickness of about 100 nm or more.
 92. The article of claim 49, whereinthe continuous layer has a thickness of about 200 nm or more.
 93. Thearticle of claim 49, wherein the continuous layer has a thickness ofabout 300 nm or more.
 94. The article of claim 49, wherein thecontinuous layer has a thickness of about 500 nm or more.
 95. Thearticle of claim 49, wherein the continuous layer has a thickness ofabout 1,000 nm or more.
 96. The article of claim 49, wherein thecontinuous layer has a thickness of about 1,500 nm or more.
 97. Thearticle of claim 49, wherein the layer has a thickness of about 2,000 nmor more.
 98. The article of claim 49, wherein the continuous layer hasan optical retardation of about 1 nm or more for light of wavelength λpropagating through the continuous layer along an axis, wherein λ isbetween 150 nm and 2,000 nm.
 99. The article of claim 49, wherein thecontinuous layer has an optical retardation of about 2 nm or more forlight of wavelength λ propagating through the continuous layer along anaxis, wherein λ is between 150 nm and 2,000 nm.
 100. The article ofclaim 49, wherein the continuous layer has an optical retardation ofabout 5 nm or more for light of wavelength λ propagating through thecontinuous layer along an axis, wherein λ is between 150 nm and 2,000mm.
 101. The article of claim 49, wherein the layer has an opticalretardation of about 10 nm or more for light of wavelength λ propagatingthrough the composite layer along an axis, wherein λ is between 150=nand 2,000 nm.
 102. The article of claim 49, wherein the layer has anoptical retardation of about 20 nm or more for light of wavelength λpropagating through the composite layer along an axis, wherein λ isbetween about 150 nm and about 2,000 nm.
 103. The article of claim 49,wherein the layer has an optical retardation of about 50 nm or more forlight of wavelength λ propagating through the composite layer along anaxis, wherein λ is between about 150 nm and about 2,000 nm.
 104. Thearticle of claim 49, wherein the layer has an optical retardation ofabout 2,000 nm or less for light of wavelength λ propagating through thecomposite layer along an axis, wherein λ is between about 150 nm andabout 2,000 nm.
 105. The article of claim 49, wherein the layer has anoptical retardation of about 1,000 nm or less for light of wavelength λpropagating through the composite layer along an axis, wherein λ isbetween about 150 nm and about 2,000 mm.
 106. The article of claim 49,wherein λ is between about 400 nm and about 700 nm.
 107. The article ofclaim 49, wherein λ is between about 510 nm and about 570 mm.
 108. Thearticle of claim 49, wherein the continuous layer has an opticalretardation of about 4 nm or more for light of wavelength λ propagatingthrough the continuous layer along an axis, wherein λ is between about400 nm and about 700 nm.
 109. The article of claim 49, furthercomprising a second continuous layer including rows of a third materialalternating with rows of a second nanolaminate material, wherein thesecond continuous layer is birefringent for light of wavelength λpropagating through the second continuous layer along the axis.
 110. Thearticle of claim 109, further comprising additional form birefringentlayers, wherein each of the form birefringent layers are birefringentfor light of wavelength λ propagating through each form birefringentlayer along the axis.
 111. An article, comprising: a form birefringentoptical retardation film comprising a nanolaminate material.